/*
* The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
* (the "License"). You may not use this work except in compliance with the License, which is
* available at www.apache.org/licenses/LICENSE-2.0
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
* either express or implied, as more fully set forth in the License.
*
* See the NOTICE file distributed with this work for information regarding copyright ownership.
*/
/**
* Set of evictors for evicting or moving blocks to other locations.
*
* The main entry point is {@link alluxio.worker.block.evictor.Evictor} which returns an evictor by
* calling alluxio.worker.block.Evictor.Factory#create.
*
* <h2>Evictor</h2>
*
* All evictors implement {@link alluxio.worker.block.evictor.Evictor} interface. In order to evict
* blocks by different policies, each evictor only need to implement
* {@link alluxio.worker.block.evictor.Evictor#freeSpaceWithView(long,
* alluxio.worker.block.BlockStoreLocation, alluxio.worker.block.BlockMetadataManagerView)}
* method. When this method is called, blocks will be evicted or moved if no enough space left.
*
* <h3>Cascading Eviction</h3> Cascading Eviction means evict blocks recursively and is only called
* in {@link alluxio.worker.block.evictor.Evictor#freeSpaceWithView(long,
* alluxio.worker.block.BlockStoreLocation, alluxio.worker.block.BlockMetadataManagerView)}
* method. Cascading Eviction will try to free space in next tier view where blocks need to be
* transferred to, if the next tier view does not have enough free space to hold the blocks, the
* next next tier view will be tried and so on until the bottom tier is reached, if blocks can not
* even be transferred to the bottom tier, they will be evicted, otherwise, only blocks to be freed
* in the bottom tier will be evicted.
*
* For example,
* {@link alluxio.worker.block.evictor.LRUEvictor#cascadingEvict(long,
* alluxio.worker.block.BlockStoreLocation,EvictionPlan)}
* is an implementation of Cascading Eviction.
*
* <h3>Eviction Plan</h3>
*
* Eviction plan will be returned when
* {@link alluxio.worker.block.evictor.Evictor#freeSpaceWithView(long,
* alluxio.worker.block.BlockStoreLocation, alluxio.worker.block.BlockMetadataManagerView)}
* is called. The eviction plan will return two block lists, one is the blocks to be removed
* directly and another is the blocks to be moved to lower tier views.
*/
package alluxio.worker.block.evictor;